Pyrometallurgical process for producing metallic copper from copper sulfide concentrates

ABSTRACT

The invention utilizes a modified Peirce-Smith converter to smelt copper sulfide concentrates and to produce flue gases sufficiently high in SO2 content to be useful for the production of sulfuric acid, thereby avoiding the usual air pollution associated with reverberatory smelting. Copper concentrates and flux are continuously fed above and onto the surface of a high grade copper matte produced and maintained in a conventional Peirce-Smith type of converter modified for the purpose. The molten material is blown with oxygen-enriched air, and smelting heat is attained by the exothermic heat of the reaction and by supplying and burning fluid fuel above the molten bath. Periodically, feed and blowing are halted and excess matte and/or slag separately skimmed off, the matte being charged into a separate converter for blowing with air in the usual manner. The slag is treated to recover most of its copper content by milling or by pyrometallurgical cleaning in a separate furnace.

United States Patent [191 Themelis et a1.

[ Nov. 26, 1974 Conn; Russell R. Beck; John V. Wagner, both of Salt LakeCity,

Utah

[73] Assignee: Kennecott Copper Corporation,

New York, NY.

22 Filed: Apr. l8, 1973 [21] Appl. No.: 352,723

[52] US. Cl 75/74, 75/72, 75/76 [51] Int. Cl C22b 15/00 [58] Field ofSearch 75/72, 74,- 76, 73, 75; 266/35, 41

[56] References Cited UNITED STATES PATENTS 3,139,336 6/1964 Dean 75/763,281,236 10/1966 Meissner 75/73 3,437,475 4/1969 Themelis et a1. 75/763,473,918 10/1969 Foard 75/74 3,627,510 12/1971 Vogt et a1. 75/76Primary ExaminerWalter R. Satterfield Attorney, Agent, 0rFirm-Mallinckrodt & Mallinckrodt 57 ABSTRACT The invention utilizes amodified Peirce-Smith con verter to smelt copper sulfide concentratesand to produce flue gases sufficiently high in SO content to be usefulfor the production of sulfuric acid, thereby avoiding the usual airpollution associated with reverberatory smelting. Copper concentratesand flux are continuously fed above and onto the surface of a high gradecopper matte produced and maintained in a conventional Peirce-Smith typeof converter modified for the purpose. The molten material is blown withmost of its copper content by milling or by pyrometallurgical cleaningin a separate furnace.

7 Claims, 3 Drawing Figures P T T IIIIvzs I974 50,520

F/G CONCENTRATES AND FLUX BURNER BURNER HIGH GRADE MATTE RADE (l P(70%10 80"/ b 2 8? Y ll weight GUS BLow BLOW (0xYGEN- (OXYGEN- ENRICHEDAIR) ENRICHED AIR) TO SULFURIC ACID PRoDUCTIoN F/G FLUE GASES (Y /O-Q /os0 BURNER SLAG 4 /5 HIGH GRADE MATTE (70% f0 80% by weigh) Cu.)

SLAG (SKIMMED TwICE PER CYCLE) MATTE /4 CooLING PIT MILLING CONCENTRATESHIGH GRADE MATTE RECIRCUL TED (70% 1o 80% by BLOW weIght Cu.) BLOW (AIR)(AIR) I AILINGS DI sCARDED METALLIC COPPER SMALL AMOU SLAG RECIRCPYROMETALLURGICAL PROCESS FOR PRODUCING METALLIC COPPER FROM COPPERSULFIDE CONCENTRATES BACKGROUND OF THE INVENTION 1 Field The inventionis in the field of processes for the smelting of copper sulfideconcentrates to produce a copper matte (Cu S, FeS) and for theconverting of such matte to metallic copper by blowing with air,yielding flue gases which are sufficiently concentrated in sulfurdioxide to be useful in the production of sulfuric acid.

2. State of the Art It has been customary in the production of themetallic copper from copper sulfide ores to subject flotationconcentrates derived from such ores to smelting in reverberatoryfurnaces for obtaining low grade (e.g., 20-40 percent Cu) copper matte,and, thereafter, to convert such copper matte to impure metallic copperin Peirce-Smith Converters, which are cylindrical vessels each equippedwith a hood and mouth through which the molten matte is periodicallycharged from a ladle transferred by crane from a reverberatory furnace.The converter is equipped with tuyeres through which air is normallyblown into the matte. The resulting gases, high in S0,, content, aredischarged through the mouth of the converter into a flue for passage toa sulfuric acid plant.

Even though air pollution from the converters has been largely avoidedby utilizing the offtake gases therefrom for the production of sulfuricacid, the offtake gases from the reverberatory smelting furnaces are toodilute in sulfur dioxide to be so utilized. Thus, they are customarilydischarged into the atmosphere, with consequent undesirable airpollution.

Some of the disadvantages of reverberatory smelting have been overcomeby a continuous process carried out in a single reactor vessel, see US.Pat. No. 3,437,475 granted to Nickolas J. Themelis and Paul Spira onApr. 8, 1969. However, such a process requires a large capitalinvestment in new equipment and is, therefore, economically notpractical for existing smelters equipped with reverberatory furnaces andPeirce-Smith converters. The same is true of other continuous processes,such as disclosed in US. Pat. No. 3,281,236 granted to Herman P.Meissner on Oct. 25, 1966.

Attempts have been made in the past to smelt copper concentrates in aconverter by means of oxygen injection. However, these have been largelyunsuccessful because the converter has been used as a batch convettingvessel, without providing auxiliary heat. Thus, oxygen utilizationefficiency has been low and control of the system haphazard, since theoperators have had no way of compensating for the large heat lossesencountered during emptying and refilling the converter with matte. I

In addition, such schemes have been based on the availability of seed"matte to start the cycle, which has meant that the use of reverberatoryfurnaces has been essential.

' SUMMARY OF THE INVENTION ,In accordance with the present invention,smelting of a copper concentrate together with a silica flux IS carriedout on a semi-continuous basis in a conventional converter vessel by theprovision of a burner above the molten bath for the injection andburning of a fluid fuel, such as fuel oil, a gaseous fuel, or a streamof dispersed coal dust. A high grade matte (approximately within therange of from to percent by weight Cu) is maintained in the converter byproperly balancing rates of material feed, fuel feed to the bumer, andblowing of the matte with oxygen-enriched air, as well as the degree ofoxygen-enrichment of such air.

The feed of concentrate and flux, the burning of fuel above the bath,and the blowing with oxygen-enriched air are continuous, except at suchtimes as matte and/or slag are being skimmed off. The level of matteneed never drop below a given minimum level, which is based on optimumutilization of the oxygen supplied with the air. This means highersmelting capacity per pound of oxygen than has heretofore been the casein conventional oxygen smelting procedures.

Slag skimmed off from the smelting converter will contain an amount ofcopper to make subsequent treatment, e.g., by casting into pits,cooling, and milling, economically possible for copper recovery. Copperloss in the tailings from the milling procedure is normally no more thantakes place in the ordinary reverberatory slag.

Matte near the white metal stage is drawn off from the smeltingconverter and transferred to a standard converter to be finished by theusual blowing with air to metallic copper. It is possible at this stageto add precipitate (cement) copper or other cold dope for melting andmerging with the converter copper produced from the matte.

In contrast with the prior art, the present invention is based on theutilization of existing Peirce-Smith converters, which, with minimummodification and expenditure, can be made adequate to carry out thesmelting duty of the usual reverberatory furnaces and to also perform apreliminary converting function. This invention, therefore, eliminatesthe need for reverberatory. furnaces, thus resulting in great reduction.in fuel and operating costs. Existing reverberatory furnaces may bedismantled to provide plant area for other purposes or may be merelyleft idle, thereby eliminating undesirable air pollution. The additionalS0 of high concentration provided by the smelting converters willprovide additional feed for existing sulfuric acid plants normallyoperated in conjunction with copper converting facilities. In thepresent process, matte from the reverberatory is not necessary since theauxiliary fuel burner can be used to smelt an initial matte batch andfrom thereon the process is self-sustaining.

THE DRAWING The best mode presently contemplated for carrying out theinvention is illustrated in the accompanying converting operation ofFIG. 2 are handled for each operating cycle of the process.

' DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT The invention can becarried out in existing converter facilities of copper producing plantsby making minor modifications in the conventional converters making uppart of the production facilities of such plants. Most modern facilitiesutilize the Peirce-Smith type of converter. Such a converter can bereadily modified for practice of the combined smelting and convertingstage of the present process. In fact, such a converter may not evenrequire modification if equipped with a so-called Garr gun, as is oftenprovided forthe introduction of flux, and with an end port in which aburner can be installed. Under such circumstances, it is only necessryto provide an appropriate supply of a mixture of copper concentrate andflux for the gun, a burner and a fuel supply therefor, and oxygeninjection facilities for blower air supplied to the converter tuyeres.This is all well within the skill of the art. If desired, feed of copperconcentrate and flux can be accomplished through the usual converterhood and mouth, the minor modification required to permit this beingalso well within the skill of the art. The normal function of the mouthand hood in discharging offtake gases from the converter into the flueprovided for same is maintained; and such gases are preferably treatedin customary manner for the production of sulfuric acid in the usualsulfuric acid plant, since the combined smelting and converting producesS of sufficient concentration for the purpose.

A diagramatic representation of such a modified Peirce-Smith converteris designated 10 in the figures of the drawing. A molten bath of coppermatte 11 is maintained within such converter 10 at all times in minimumdepth sufficient to adequately cover .the tuyeres for efficient blowing.FIG. 1 illustrates the converter at the end of one cycle of operationand about to start another cycle, it being preferred to continue theinjection of fuel above the matte 11 between cycles to maintain propertemperature of the molten bath.

The matte 11 is of high grade,,.having a copper con tent approximatelywithin the range of white metal, rather than the usual low grade matte(from 20 to percent by weight) normally fed to a converter from thereverberatory furnace. The term white metal as used herein denotes CuS.FeS, having a copper content within the range of about 70 to 80percent by weight. For the combined smelting and converting stage of theprocess as shown in FIG. 2, a copper ore concentrate derived in theusual manner by flotation and preferably formed into green pellets tominimize dust after haaving been mixed with the usual silica flux, isfed into the converter 10 either through the usual hood modified for thepurpose as indicated above or through a Garr gun, heat additional to thenormal exothermic provided by the reaction being supplied in the space12 above the white metal by means of a suitable burner, as previouslymentioned and as indicated. Fuel supplied to the burner in any suitablemanner is burned above the bath to supply the additional smelting heatrequired over and above that provided by the exothermic heat of theconverting reaction that goes on simultaneously with the smeltingreaction-in the converter 10.

For converting purposes, the molten bath of high grade matte 11 is blownin conventional manner, but with oxygen-enriched air rather than withthe usual atmospheric air alone. Oxygen enrichment is typically withinthe range of 25 to 35 percent oxygen concentration.

As indicated in FIG. 3, slag 13 is periodically skimmed from the top ofthe molten bath 11 during the smelting and converting stage, twice percycle being normal practice. The slag contains about 5 to 8 percent Cuby weight as compared to about 0.35 percent for reverberatory furnaceslag and about 10 to 12 percent for continuous smelting and convertingprocesses carried out in a single reaction vessel. Thus, such slag iswell suited for treatment by milling or pyrometallurgical treatment forrecovery of its copper content. For the purpose of milling, the moltenslag 11 is advantageously run into a cooling pit for solidification andcooling and is then treated by the usual crushing, grinding, andflotation to produce copper concentrate for recirculation into the feedof the present overall process and tailings for discard as waste.

For each cycle of the process, excess matte is drawn off from the moltenbath of white metal, as indicated in FIG. 3, and is transferred to astandard copper converter 14 for additional blowing with air incustomary manner to produce metallic. copper with a minimum of slag, ifany. Such slag as may be formed is recirculated to the smeltingconverter 10. An adequate amount of the white metal matte 11 is left inthe smelting converter 10 to cover the tuyeres for effective utilizationof the oxygen in the oxygen-enriched air blown through such tuyeres.

The white metal matte drawn off from the combined smelting andconverting vessel 10 is preferably transferred to converter 14 by aconventional ladle, and is blown in such converter 14 in customarymanner with air alone.

Metallic copper is drawn off periodically from the finishing converter14 and represents the final product of the process. If desired, cementcopper or other copper dope may be added to the molten bath in finishingconverter 14 for melting and for thereby increasing output of metalliccopper.

Although this cyclic process is semi-continuous, experience has shownthat the non-blowing periods, during which excess matte and/or slag aredrawn off from the smelting converter 10 are relatively short incomparison to the total blowing time, which can be over percent ofoperating time. Accordingly, the heat loss per ton of metallic copperproduced has been shown to be less than in conventional oxygen smeltingpractice.

EXAMPLE the enriched air injected into the converter could be controlledat a constant level of from 21 to 35 percent oxygen.

In a typical test run, an initial charge of molten white metal mattecontaining 71% Cu was run into the con-' verter to a depth adequatelysubmerging the tuyere openings, and fuel input to the burner wascontrolled manually on the basis of readings from a radiamatic pyrometerfocused on the molten bath surface.

A mixture of moist copper sulfide flotation concentrate and a silicaflux was charged continuously into the converter through the specialhood opening at the rate of 40 tons/hour while simultaneously blowingthe molten matte with oxygen-enriched air averaging 29 percent oxygenand while operating the burner on a normal basis. The feed ofconcentrates, flux, and oxygenenriched air was continued along withoperation of the burner until the molten bath, containing matte andslag, filled the converter to its maximum operating level. The feed ofore concentrates, flux, and oxygenenriched air was then discontinued andthe molten bath allowed to settle into a supernatent layer of slag and amolten pool of copper matte while still operating the burner. Thesupernatant layer of slag was then skimmed from the converter whilecontinuing to operate the bumer at a reduced firing rate and coppermatte was withdrawn, leaving a pool of copper matte in the converter ofsufficient depth to adequately submerge the tuyere openings.

The processing cycle was repeated until 406 tons of dry concentrate hadbeen smelted and converted to copper matte containing approximately 75percent copper by weight.

The average composition of slag removed from the converter was 5% Cu and26% SiO The average fuel consumption (natural gas) during the testperiod was 0.56 million B.T.U. per ton of dry concentrate, and theconsumption of oxygen was 0.14 tons per ton of dry concentrate smelted.

The gases removed from the converter dumg the process varied from 7 to9% S0 after hood dilution and were processed in a conventional sulfuricacid plant. A slag sample from the converter was cooled and milled intoa concentrate containing 26.4% Cu. The tailings from the milling of theslag contained less than 0.25 percent copper by weight.

The tests showed that it is practical to adapt existing copperconverting facilities to the present process and that copper smeltingand converting can be carried out to meet new anti-pollutionregulations, with very small capital outlay.

Operation of similar Peirce-Smith converter facilities on a commercialtest basis handling concentrate and flux feed at a rate of approximately500 tons per day has further substantiated the capabilities of theprocess of this invention.

Whereas this invention is here specifically illustrated and describedwith respect to a certain preferred form thereof, it is to be understoodthat variations are possible without departing from the inventiveconcepts particularly pointed out in the claims that follow.

We claim:

1. A pyrometallurgical process for producing metallic copper from coppersulfide concentrates, comprising substantially continuously feeding acopper fulfide concentrate and a flux therefor into a conventional,airblow, copper converter vessel, said vessel containing a high quality,molten bath that, except for accumulating slag and still unmelted feed,consists substantially only of high grade copper matte having a coppercontent approximately within the range of about percent to about percentcopper and a depth at least covering the tuyere openings so as to beadequate for blowing; blowing said bath with oxygen-enriched air havingan oxygen content within the range of about 25 percent to about 35percent by weight, while introducing and maintaining above said bathsufficient heat additional to the exothermic heat of reaction of thebath to effect smelting of said concentrate and flux, the said feeding,blowing with air, and introducing of additional heat, and the degree ofoxygen enrichment of said air, being controlled to substantiallymaintain the said high quality of the molten bath of copper matte;periodically halting the continuous feeding and the blowing end, duringthe halting periods, skimming off from said bath either slag alone orboth slag and matte, the quantity of matte skimmed off beingsubstantially no more than will leave said bath of matte sufficientlydeep to cover the tuyere openings for blowing purposes, whereby thesmelting reaction condition is maintained within said converter vesselfrom skimming period to skimming period; continuing the continuousfeeding of copper sulfide concentrates, the blowing of said bath withsaid oxygen-enriched air, the introduction of additional heat, and thecontrol thereof between the skimming periods; and treating the matteskimmed off from said converter vessel in a separate converter vesselfor the production of metallic copper.

2. A process in accordance with claim 1, wherein the copper oreconcentrate fed into the converter. vessel has a moisture contentapproximately with the range of from 7 to 12 percent by weight.

3. A process in accordance with claim 1, wherein cement copper is addedto the charge of white metal matte in the separate converter.

4. A process in accordance with claim 1, wherein the feed is introducedinto the converter above, and is deposited onto, the superficial surfaceof the bath.

5. A process in accordance with claim 1, wherein the slag has a coppercontent of about 5 percent to about 8 percent and including theadditional step of treating the slag for the recovery of its coppercontent.

6. A process in accordance with claim 5, wherein the slag is reduced tofinely divided condition as a flotation feed and is treated by flotationfor recovery of a copper concentrate.

7. A process in accordance with claim 6, wherein the copper concentratefrom the slag is recirculated to the smelting converter.

P0405) UNITED STATES PATENT OFFICE t QQERTIFICATE 0F CORRECTION PatentNo; 3, 850; 620 Dated November 26, 1974 Inventor(s) Nickolas JohnThemelis et a1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 6, at the end of line 4, the word "fulfide" should be sulfide andat the end of line 23,

the Word 'fend" should be and Signed and sealed this 21st day of January1975.

LSEAL) Attest:

MCCOY M. GIBSON JR. '6. MARSHALL DANN Attesting Officer Commlssloner ofPatents

1. A PYROMETALLURGICAL PROCESS FOR PRODUCING METALLIC COPPER FROM COPPERSULFIDE CONCENTRATES, COMPRISING SUBSTANTIALLY CONTINUOUSLY FEEDING ACOPPER FULFIDED CONCEBTRATE AND A FLUX THEREOF INTO A CONVENTIONAL,AIR-BLOW COPPER CONVERTER VESSEL, SAID VESSEL CONTAINING A HIGH QUALITY,MOLTEN BATH THAT, EXCEPT FOR ACCUMULATING SLAG AND STILL UNMELTED FEED,CONSISTS SUBSTANTIALLY ONLY OF HIGH GRADE COPPER MATTE HAVING A COPPERCONTENT APPROXIMATELY WITIN THE RANGE OF ABOUT 70 PERCENT TO ABOUT 80PERCENT COPPER AND A DEPTH AT LEAST CONVERTING THE TUYERS OPENINGS SO ASTO BE ADEQUATE FOR BLOWING; BLOWING SAID BATH WITH OXYGEN-ENRICHED AIRHAVING AN OXYGEN CONTENT WITHIN THE RANGE OF ABOUT 25 PERENT TO ABOUT 35PERCENT BY WEIGHT, WHILE INTRODUCING AND MAINTAINING ABOVE SAID BATHSUFFICIENT HEAT ADDITIONAL TO THE EXOTHERMIC HEAT OF REACTON OF THE BATHTO EFFECT SMELTING OF SAID CONCENTRATE AND FLUX, THE SAID FEEDINGBLOWING WITH AIR AND INTRODUCING OF ADDITIONAL HEAT, AND THE DEGREE OFOXYGEN ENRICHMENT OF SAID AIR BEING CONTROLLED TO SUBSTANTIALLY MAINTAINTHE SAID HIGH QUALITY OF THE MOLTEN BATH OF COPPER MATTE; PERODICALLYHALTING THE CONTINUOUS FEEDING AND BLOWING END, DURING THE HALTINGPERIODS, SKIMMING OFF FROM SAID BATH EITHER S2LAG ALONE OR BLOTH SLAGAND MATTE, THE QUANTITY OF MATTE SKIMMED OFF BEING SUBSTANTIALLY NO MORETHAN WILL LEAVE SAID BATH OF MATTER SUFFUCUENTLY DEEP TO COVER THETUYERE OPENINGS FOR BLOWING PURPOSES, WHEREBY THE SMELTING REACTIONCNDITION IS MAINTAINED WITHIN SAID CONVERTER VESSEL FROM SKIMMING PERIODTO SKIMMING PERIOD; CONTINUING THE CONTINUOUS FEEDING OF COPPER SULFIDECONCENTRATES, THE BLOWING OF SAID BATH WITH SAID OXYGEN-ENRICHED AIR,THE INTRODUCTION OF ADDITIONAL HEAT, AND THE CONTROLLED THEREOF BETWEENTHE SKIMMING PERIODS; AND TREATING THE MATTE SKIMMED OFF FROM SAIDCONVERTER VESSEL IN A SEPARATE CONVERTER VESSEL FOR THE PRODUCTION OFMETALLIC COPPER.
 2. A process in accordance with claim 1, wherEin thecopper ore concentrate fed into the converter vessel has a moisturecontent approximately with the range of from 7 to 12 percent by weight.3. A process in accordance with claim 1, wherein cement copper is addedto the charge of white metal matte in the separate converter.
 4. Aprocess in accordance with claim 1, wherein the feed is introduced intothe converter above, and is deposited onto, the superficial surface ofthe bath.
 5. A process in accordance with claim 1, wherein the slag hasa copper content of about 5 percent to about 8 percent and including theadditional step of treating the slag for the recovery of its coppercontent.
 6. A process in accordance with claim 5, wherein the slag isreduced to finely divided condition as a flotation feed and is treatedby flotation for recovery of a copper concentrate.
 7. A process inaccordance with claim 6, wherein the copper concentrate from the slag isrecirculated to the smelting converter.